A polygon connected three-phase autotransformer using nine windings per phase provides a reduced power rating fifteen-phase power source suitable for 30-pulse AC to DC power converters. The windings are selected and connected in a manner that accommodates zero-sequence currents, such as the third harmonic, and minimizes total kVA rating. When the autotransformer is used to power a 15-phase AC to DC converter its kVA rating is typically less than 51% of the DC load kW. AC line current distortion is negligible and can satisfy the most exacting practical harmonic specifications. Additional isolated windings can provide means for the invention to operate as an efficient double-wound transformer.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An autotransformer for converting three-phase AC power to fifteen-phase AC power comprising: a. three coils each containing serial windings and non-serial windings; b. said serial windings and non-serial windings totaling at least nine in number; c. said serial windings and non-serial windings being magnetically coupled; d. said serial windings and non-serial windings on said three coils being interconnected to form a multi-sided polygon; e. said multiple-sided polygon having multiple nodes to which connections can be made; f. said multiple nodes including symmetrically disposed nodes; g. said symmetrically disposed nodes providing points for applying three-phase AC input voltage and extracting AC output voltages of predetermined amplitude and phase; h. wherein predetermined AC output voltages may be less than greater than or equal to that of the three-phase AC input voltage.
2. The autotransformer of claim 1 wherein the input voltage is a three-phase AC supply and the output is a fifteen-phase AC supply with voltages nominally equal in amplitude and typically spaced by 24°.
3. The autotransformer of claim 1 with an additional isolated winding on each coil to provide a closed delta circuit.
4. The autotransformer of claim 1 with one or more additional non-isolated windings to provide one or more closed delta circuits.
5. The autotransformer of claim 1 with an additional isolated winding on each coil such that three phase AC input power may be applied through such isolated windings to convert the autotransformer to a double-wound transformer.
6. The autotransformer of claim 2 wherein a fifteen-phase output is connected to a 15-phase rectifying device so as to produce a 30-pulse converter with low output voltage ripple on the DC voltage and with low harmonic distortion of the AC input harmonic current.
7. The autotransformer of claim 2 wherein series reactance is included in the three phase AC input power source as to further attenuate high frequency harmonic currents that may be associated with a multi-pulse AC to DC converter.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
May 4, 2009
May 18, 2010
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